Amphoteric cationic polymers for controlling deposition of pitch and stickies in papermaking

ABSTRACT

The present invention relates to a method and composition for controlling pitch and stickies deposit in a pulp and papermaking process using amphoteric copolymers of diallyldimethylammonium chloride (DADMAC) with acrylic acid and/or acrylamide and optionally a siliceous material.

This application claims the benefit of Provisional Application No. 60/585,184, filed Jul. 2, 2004 and Provisional Application No. 60/662,755, filed Mar. 17, 2005.

The present invention relates to a method for controlling pitch and stickies deposition in a pulp and papermaking process using amphoteric copolymers formed from the monomers diallyldimethylammonium chloride (DADMAC), acrylic acid and optionally acrylamide. The method may optionally further comprise the addition of a siliceous material. The pitch and stickies are found in mechanical pulps, recycled fiber, coated broke, white water and the like. The invention also encompasses a composition for pitch and stickies control in papermaking comprising the amphoteric copolymer and optionally, a siliceous material.

BACKGROUND OF THE INVENTION

The present invention is directed to the use of amphoteric copolymers or terpolymers of diallyldimethylammonium chloride (DADMAC) with acrylic acid and optionally acrylamide for controlling and preventing deposition of pitch and stickies in papermaking. The amphoteric copolymer may otionally, further comprise a siliceous material.

The siliceous material may be any of the materials selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites and swelling clays. This siliceous material may be in the form of an anionic microparticulate material. When the siliceous material is a swelling clay it may typically be a bentonite type clay.

Cationic polymers have been used extensively in paper making as flocculants for improving retention and drainage and as coagulants or fixatives to control anionic trash and deposition of pitch and stickies. Among the most important and extensively used cationic polymers for deposit control are the quaternary ammonium polymers of diallyidialkyl ammonium compounds (e.g., DADMAC) and copolymers of epichlorohydrin and dimethylamine known as polyamines. Homopolymers of DADMAC and polyamines with high cationic charge density are good for neutralizing anionic trash but have limited success for controlling pitch and stickies deposition. There is still a need for polymer compositions which will prevent pitch and stickies deposition.

Pitch and stickies are interfering substances in the wet end of papermaking that can affect both the machine runnability and paper quality. The term “pitch” used here refers to a colloidal dispersion of wood-derived hydrophobic particles released from the fibers during a pulping process and is also called wood pitch. Wood pitch includes fatty acids, resin acids, their insoluble salts, and esters of fatty acids with glycerol, sterols, and other fats and waxes. The hydrophobic components of pitch, particularly triglycerides, are considered one of the major factors determining whether the presence of such pitch will lead to deposit problems. Deposit-forming pitch often contains significantly high amounts of triglyciderides.

The term “stickies” used herein refers to sticky materials and interfering substances that arise from components of recycled fibers, such as adhesives and coatings. Stickies can come from coated broke, recycled waste paper for board making and de-inked pulp (DIP). The stickies from coated broke is sometimes called white pitch. Deposition of pitch and stickies often leads to defects in the finished product and paper machine downtime causing lost profits for the mill. These problems become more significant when paper mills “close up” their process water systems for conservation and environmental reasons. Unless the pitch and stickies are continuously removed from the system in a controlled manner, these interfering substances will accumulate and eventually lead to deposition and runnability problems. Technology in place today is based on fixing the pitch or stickies to the fibers before they have a chance to agglomerate, or alternatively coating the pitch or stickies with a polymer that makes them non-tacky and therefore unable to agglomerate.

Three chemical methods are commonly used by paper mills to control pitch and stickies deposit:

-   -   1) detackification     -   2) stabilization     -   3) fixation.         These methods are, however, not commonly used together since         they may conflict with each other. In detackification, a         chemical is used to build a boundary layer of water around the         pitch and stickies to decrease depositability. Detackification         can be achieved by addition of pitch adsorbents such as talc and         bentonite. However, pitch adsorbents such as talc can end up         contributing to the pitch deposit problem if the talc/pitch         particles are unable to be retained in the paper sheet with         surfactants and water-soluble polymers. In stabilization,         surfactants and dispersants are used to chemically enhance         colloidal stability and allow pitch and stickies to pass through         the process without agglomerating or depositing.

In fixation, polymers are used to fix pitch and stickies to the fiber and remove them from the white water system. The interfering substances in papermaking systems are usually anionic in nature and are sometimes referred to as anionic trash or cationic demand. Anionic trash consists of colloidal (pitch and stickies) and dissolved materials that adversely affect the paper making in a variety of ways through deposit formation or interference with chemical additives. Removal of anionic trash by reducing cationic demand with a cationic polymer is a way of deposit control through fixation. The advantage of using cationic polymeric coagulants for pitch and stickies control is that the pitch and stickies are removed from the system in the form of microscopic particles dispersed among the fibers in the finished paper product.

Cationic polymers are normally used as fixatives to control pitch and stickies through fixation. Nonionic polymers discussed in PCT Application No. 200188264 such as polyvinyl alcohol and copolymers such as polyacrylamide-vinyl acetate have been developed and used for stickies control through detackification. U.S. Pat. No. 6,051,160 discloses hydrophobically modified anionic polymers such as a copolymer of styrene and maleic anhydride for used in pitch deposit control through, most likely, the pitch stabilization mechanism.

Homopolymers of DADMAC are commonly used alone or with other components as fixatives for anionic trash control and pitch control.

Canadian Patent No. 1,194,254 teaches a method of reducing wood pitch particles in aqueous pulp with a polyDADMAC. The patent does not teach use of the polyDADMAC for stickies containing pulps from recycled secondary fibers. Papermakers today face the increased use of recycled secondary fiber. Unlike virgin fiber that was used in the past, recycled fibers contain stickies from many sources such as glue, adhesives and coating binders. The Canadian patent is also limited to use of DADMAC homopolymer. U.S. Pat. No. 5,989,392 teaches use of crosslinked DADMAC polymers for controlling anionic trash and pitch deposition in pulp containing broke. A pulp filtrate turbidity test is used to evaluate polymer performance in pitch deposition control therein. Improved efficiencies of solution crosslinked or branched polyDADMACs over conventional linear polyDADMAC are demonstrated. The crosslinked or branched polyDADMACs used are prepared using a polyolefinic crosslinking monomer such as triallylamine hydrochloride or methylene bisacrylamide.

U.S. Pat. No. 4,964,955 discloses a method of using an aqueous slurry of polyDADMAC and kaolin clay for reducing pitch in pulping and papermaking.

U.S. Pat. No. 4,913,775 provides a process wherein a water soluble substantially linear cationic polymer is applied to the paper making stock prior to a shear stage and then reflocculating by introducinting bentonite after that shear stage. This process provides enhanced drainage and also good formation and retention. This process which is commercialized by Ciba Specialty Chemicals under the HYDROCOL trade mark has proved successful for more than a decade. This process however, relates to retention and drainage, not pitch and sticky deposit control. The bentonite and cationic polymer are normally added to the thin stock in the papermaking process.

U.S. Pat. No. 4,795,531 describes a method of making paper in which a low molecular weight cationic organic polymer is added to the furnish and then a colloidal silica and a high molecular weight charged acrylamide copolymer of molecular weight of at least 500,000.

U.S. Pat. No. 5,256,252 discloses a method for controlling pitch deposit using enzyme (lipase) with DADMAC polymers. This patent is related more to use of enzyme which is a necessary component for the method. A filtrate turbidity test is used to evaluate pitch control performance.

U.S. Pat. No. 5,230,774 is directed to a process for controlling pitch deposits by adding a blend of a homopolymer of DADMAC and ammonium zirconium carbonate. None of the polymers are copolymers of DADMAC.

U.S. Pat. No. 5,131,982 teaches use of DADMAC homopolymers and copolymers for coated broke treatment to control white pitch. The patent teaches a method of adding DADMAC polymer to re-pulped coated broke and then admixing the treated coated broke pulp with other fiber sources before forming a paper sheet. Use of DADMAC polymers for pitch and stickies control for mechanical pulp and deinked recycled pulp is not taught. The copolymers claimed are mainly copolymers of DADMAC and acrylamide with more than 25% of acrylamide.

Amphoteric polymers are polyelectrolytes containing both positive and negative functional groups in the same polymer molecule. Amphoteric DADMAC polymers are DADMAC copolymers containing negative, or potentially negative, functional groups.

European Application No. 464,993 discloses use of an amphoteric copolymer of DADMAC and acrylic acid salts for controlling wood pitch deposition or natural pitch. A filtrate turbidity test is one of the test methods used to evaluate pitch deposit control performance. The polymers disclosed are not claimed for use in deposit control of stickies and white pitch in recycle pulps and coated broke. The amphoteric DADMAC terpolymer claimed does not include polymers containing acrylamide.

PCT Application No. 200034581 teaches use of amphoteric terpolymers of DADMAC, acrylamide and acrylic acid as a retention/drainage/formation aid in a papermaking process. The terpolymers are also taught for controlling white pitch for coated broke. The preferred terpolymers of DADMAC, acrylamide and acrylic acid claimed for treating white pitch contain more than 25% of acrylamide and not more than 50% of DADMAC. A filtrate turbidity test is used to determine the polymers white pitch deposit control performance.

European Application No. 058622 teaches a method for reducing or preventing the deposition of wood pitch during the papermaking process with an emulsion copolymer of DADMAC, DADEAC, acrylamide and acrylic acid. The copolymer contains 45 to 50% acrylamide, no more than 50 wt % of DADMAC and at least 2 wt % of an uncommon monomer, DADEAC, (diallyldiethylammonium chloride) which is not commercially available today. No mention is made for use of the copolymer for stickies control of recycled fibers.

U.S. Pat. No. 4,505,828 teaches use of an inverse emulsion amphoteric copolymer made from acrylamide, acrylic acid and dimethylaminoethyl methacrylate in petroleum recovery by a water flooding process and in papermaking as a drainage aid. Use of a solution amphoteric terpolymer of DADMAC, acrylamide and acrylic acid is not taught. The patent is not related to pitch and stickies deposit control in papermaking.

U.S. Pat. No. 3,639,208 discloses the preparation and composition of certain amphoteric terpolymers of DADMAC, acrylamide and acrylic acid obtained by partly hydrolyzing a copolymer of acrylamide and DADMAC. The copolymer and its hydrolyzed terpolymer contains less than 70% DADMAC. The terpolymers obtained are used as retention aids in papermaking. Use of the amphoteric terpolymer for pitch control is not taught.

U.S. Pat. No. 5,837,100 teaches the use of blends of a dispersion polymer and a coagulant for coated broke treatment to improve retention and/or drainage. The water dispersion polymer is a copolymer of acrylamide and quaternary dimethylaminoethyl acrylate. The coagulant is a copolymer of epichlorohydrin and dimthylamine. Turbidity reduction testing is used to determine the activity efficiency of the polymers.

Fixatives with increased pitch and stickies fixation power are needed. Alum, starches and low molecular weight cationic coagulants conventionally used for deposit control can neutralize anionic trash and detrimental substances (pitch and stickies) and form complexes. However, they may not carry sufficient charge and/or molecular weight to fix pitch and stickies complexes to the fiber. If not strongly fixed to the fibers, the complexes will become concentrated in the system and will lead to deposition problems.

Innovations in fixatives for runnability improvement by the present inventors have led to development of a number of diallyldimethylammonium chloride (DADMAC) copolymers with high fixation power for pitch and stickies control. These DADMAC polymers have significantly greater power to remove detrimental pitch and stickies from a papermaking water system than existing commercial fixative products. When combined with siliceous material, the polymers are also effective.

The above review shows that there is a need for controlling pitch and stickies deposition in paper making with effective polymers. The search for polymer compositions which will prevent pitch and stickies deposition has met with limited success and is still ongoing. It has now been found that an amphoteric DADMAC copolymer with high DADMAC and acrylic acid (AA) units in an amount from about 0.1 to about 15% based on the weight of the DADMAC copolymer content is very effective in reducing pitch and stickies. The amphoteric polymers are effective when used on their own and when combined with siliceous material.

SUMMARY OF THE INVENTION

A dual functional polymer capable of controlling deposition through both fixation and anionic trash reduction is desirable. The inventive water-soluble amphoteric polymers described herein serve this dual purpose since they contain anionic and nonionic hydrogen bonding groups in addition to cationic functionality for fixation and charge neutralization. The polymers are also effective when combined with siliceous material.

Amphoteric polymers are polyelectrolytes containing both positive and negative functional groups in the same polymer molecule. Amphoteric DADMAC polymers are DADMAC copolymers containing negative, or potentially negative, functional groups.

One objective of this invention is to provide for pitch and stickies deposit control in papermaking an amphoteric polymer of DADMAC containing anionic groups which impart variable charge density and hydrophobicity for the polymer in response to pH change.

Another objective of this invention is to provide for pitch and stickies deposit control in papermaking an amphoteric polymer of DADMAC containing nonionic functional groups which can provide additional interactions through hydrogen bonding in addition to ionic charge interaction.

Accordingly, the invention encompasses a process for pitch and stickies deposit control in papermaking comprising

-   adding to a paper furnish -   a composition comprising an amphoteric polymer     wherein X⁻ is an anion; -   M⁺ is hydrogen, ammonium, sodium, or potassium; -   R is hydrogen or methyl; -   R₁ is methyl or ethyl; -   n is from about 70 to about 99.8%, -   m is from about 0.2 to about 30%, and -   p is from 0 to about 30%,     wherein n+m+p=100% based on the total weight of the amphoteric     polymer.

Preferably, X⁻ is Cl⁻,

-   M⁺ is Na⁺, -   n is from about 85 to about 98%, -   m is from about 1 to about 15%, and -   p is from about 1 to about 10% by weight based on the total weight     of the amphoteric polymer.

The amphoteric polymer composition may further comprise a siliceous material. The method above may further comprise the step of adding a siliceous material. The amphoteric polymer may be added before, after or simultaneously (preferably separately) a siliceous material to the furnish.

The ratio of cationic charge to anionic charge or potentially anionic charge refers to the ratio of the moles of the cationic monomer divided by the moles of the anionic monomer or potentially anionic monomer which form the amphoteric polymer.

The present inventors have discovered that a cationic amphoteric DADMAC polymer with a ratio of cationic charge to anionic charge greater than about 1.2 can be successfully used to control pitch and stickies deposit by removing them from the system in the form of microscopic particles.

The present invention is directed to application of a water-soluble cationic amphoteric polymer for controlling and preventing deposition of pitch and stickies in papermaking. The method comprises the step of adding the amphoteric polymer to treat mechanical pulp for controlling wood pitch deposits, coated broke for controlling stickies or with pitch deposit, and recycled pulp for controlling stickies deposit. The amphoteric polymer may further comprise a siliceous material.

The cationic amphoteric polymer is made by radical polymerization of DADMAC with (meth)acrylic acid and/or acrylamide.

DETAILED DESCRIPTION OF THE INVENTION

In the invention, the amphoteric polymer is any polymer containing both a cationic charge and an anionic charge. The cationic amphoteric polymer is an amphoteric polymer with a cationic charge content greater than the anionic charge. The cationic amphoteric polymer can be a copolymer of two monomers derived from cationic and anionic monomers or a terpolymer of three monomers derived from cationic, anionic and nonionic monomers.

Cationic polymers are commonly used in papermaking to remove anionic trash by charge neutralization. Anionic trash consists of colloidal (pitch and stickies) and dissolved materials that adversely affect the papermaking in a variety of ways through deposit formation or interference with chemical additives. Removal of anionic trash by fixing the colloidal particles to fiber and reducing the cationic demand with a cationic polymer is a way of pitch and stickies deposit control. The advantage of using cationic polymeric coagulants for pitch and stickies control is that the pitch and stickies are removed from the system in the form of microscopic particles dispersed among the fibers in the finished paper product.

The present inventors have discovered that the fixation of pitch and stickies to paper fiber and charge neutralization can be enhanced by the use of amphoteric copolymers with a mole ratio of cationic charge to anionic charge greater than about 1.2, preferably greater than about 4 and most preferably greater than about 5. The amphoteric copolymers are formed by polymerization of diallyldialkylammonium compounds and (meth)acrylic acid (and/or its salts) and optionally acrylamide. The preferred diallyldialkyl ammonium compounds are diallyldimethylammonium chloride (DADMAC).

For the purposes of the invention, the phrase (meth)acrylic or (meth)acrylate refers to both the acrylic and methacrylic or acrylate or methacrylate derivatives.

wherein X⁻ is an anion;

-   M⁺ is hydrogen, ammonium, sodium, or potassium; -   R is hydrogen or methyl; -   R₁ is methyl or ethyl; -   n is from about 70 to about 99.8%; -   m is from about 0.2 to about 30% -   and -   p is from 0 to about 30% with n+m+p=100% based on the total weight     of the amphoteric polymer.

Preferably, X⁻ is Cl⁻;

-   M⁺ is Na⁺; -   n is from about 85 to about 98%; -   m is from about 1 to about 15% -   and -   p is from about 1 to about 10% by based on the total weight of the     amphoteric polymer.

The unit n of the above polymer represents a unit derived from a cationic monomer selected from the group consisting of diallyidialkylammonium compounds.

For example, the cationic monomer can be a diallyldiethylammonium halide or diallydimethylammonomium halide.

The unit m of the above polymer represents a unit derived from an anionic monomer or potentially anionic monomer selected from the group consisting of hydrolysed acrylamide and (meth)acrylic acids and/or salts thereof.

The potentially anionic monomer can be hydrolysed acrylamide.

Alternatively, the anionic monomer may preferably be (meth)acrylic acid and/or salts thereof.

The amphoteric DADMAC polymer for use in accordance with the present invention is preferably one containing cationic charge in excess of the anionic charge. The molar ratio of n/m is preferably greater than about 1.2, more preferably, greater than about 4 and most preferably greater than about 5.

The amphoteric DADMAC polymer may have a weight average molecular weight ranging from about 10,000 to about 20,000,000, preferably, from about 100,000 to about 2,000,000, and more preferably from about 300,000 to about 2,000,000.

The amphoteric DADMAC polymer can be used in dosages that range from about 0.01 to about 20 lbs/ton, preferably from about 0.2 to about 10 lbs/ton based on dry solids.

Polymerization of the cationic amphoteric polymer can be carried out by aqueous solution polymerization, water-in-oil inverse emulsion polymerization or dispersion polymerization using a suitable free radical initiator. Examples of suitable initiators include persulfates such as ammonium persulfate (APS); peroxides such as hydrogen peroxide, t-butyl hydroperoxide, and t-butyl peroxy pivalate, azo initiators such as 2,2′-azobis(2-amidinopropane) dihydrochloride, 4,4′-azobis-4-cyanovaleric acid and 2,2′-azobisisobutyronitrile; and redox initiator systems such as t-butyl hydroperoxide/Fe(II) and ammonium persulfate/bisulfite. Aqueous solution polymerization using ammonium persulfate (APS) is the preferred method for preparing the cationic amphoteric polymer of the preferred monomers of DADMAC, (meth)acrylic acid and acrylamide.

(Meth)acrylic acid monomer can be used in its acid form in polymerization. The produced acid polymer solution can then be neutralized with a suitable base to the desired pH and counter ions. Alternatively, (meth)acrylic acid monomer can be partly or completely neutralized before polymerization. Examples of suitable bases for neutralization of (meth)acrylic acid monomeric units include NaOH, KOH, and (NH₄)OH.

It is preferred to carry out the polymerization in the absence of oxygen. Oxygen can be removed from the reaction medium by applying vacuum with agitation or by purging with an inert gas such as nitrogen or argon. The polymerization can then be conducted under a blanket of the inert gas.

The siliceous material may be any of the materials selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates and zeolites. This siliceous material may be in the form of an anionic microparticulate material. Alternatively the siliceous material may be cationic silica.

In one more preferred form of the invention the siliceous material is selected from silicas and polysilicates. The silica may be any colloidal silica, for instance as described in U.S. Pat. No. 4,961,825. The polysilicate may be a colloidal silicic acid as described in U.S. Pat. No. 4,388,150.

The polysilicates of the invention may be prepared by acidifying an aqueous solution of an alkali metal silicate. For instance polysilicic microgels otherwise known as active silica may be prepared by partial acidification of alkali metal silicate to about pH 8-9 by use of mineral acids or acid exchange resins, acid salts and acid gases. It may be desired to age the freshly formed polysilicic acid in order to allow sufficient three dimensional network structure to form. Generally the time of ageing is insufficient for the polysilicic acid to gel. Particularly preferred siliceous materials include polyalumino-silicates. The polyaluminosilicates may be for instance aluminated polysilicic acid, made by first forming polysilicic acid microparticles and then post treating with aluminium salts, for instance as described in U.S. Pat. No. 5,176,891. Such polyaluminosilicates consist of silicic microparticles with the aluminium located preferentially at the surface.

Alternatively the polyaluminosilicates may be polyparticulate microgels of surface area in excess of about 1000 m²/g formed by reacting an alkali metal silicate with acid and water soluble aluminium salts, for instance as described in U.S. Pat. No. 5,482,693. Typically the polyaluminosilicates may have a mole ratio of alumina:silica of between 1:10 and 1:1500.

Polyaluminosilicates may be formed by acidifying an aqueous solution of alkali metal silicate to pH 9 or 10 using concentrated sulphuric acid containing 1.5 to 2.0% by weight of a water soluble aluminium salt, for instance aluminium sulphate. The aqueous solution may be aged sufficiently for the three dimensional microgel to form. Typically the polyaluminosilicate is aged for up to about two and a half hours before diluting the aqueous polysilicate to 0.5 weight % of silica.

The siliceous material may be a colloidal borosilicate, for instance as described in WO-A-9916708. The colloidal borosilicate may be prepared by contacting a dilute aqueous solution of an alkali metal silicate with a cation exchange resin to produce a silicic acid and then forming a heel by mixing together a dilute aqueous solution of an alkali metal borate with an alkali metal hydroxide to form an aqueous solution containing 0.01 to 30% B₂O₃, having a pH of from 7 to 10.5. In one preferred aspect the siliceous material is a silica.

Preferably when the siliceous material is a silica or silicate type material it has a particle size in excess of about 10 nm. More preferably the silica or silicate material has a particle size in the range about 20 to about 250 nm, especially in the range about 40 to about 100 nm.

In a more preferred form of the invention the siliceous material is a swelling clay. The swellable clays may for instance be typically a bentonite type clay. The preferred clays are swellable in water and include clays which are naturally water swellable or clays which can be modified, for instance by ion exchange to render them water swellable. Suitable water swellable clays include but are not limited to clays often referred to as hectorite, smectites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites and sepiolites. These clays may be either naturally occurring or synthetic. An example of a synthetic hectorite clay would be LAPONITE available from Southern Clay Products, Inc., U.S.A. Typical anionic swelling clays are described in U.S. Pat. Nos. 4,753,710 and 4,913,775.

Most preferably the clay is a bentonite type clay. The bentonite may be provided as an alkali metal bentonite. Bentonites may be natural or synthetic. Naturally occurring bentonites may be either as alkaline bentonites, such as sodium bentonite or as the alkaline earth metal salt, usually the calcium or magnesium salt. Generally the alkaline earth metal bentonites are activated by treatment with sodium carbonate or sodium bicarbonate. Activated swellable bentonite clay is often supplied to the paper mill as dry powder. Alternatively the bentonite may be provided as a high solids flowable slurry of activated bentonite, for example at least about 15 or about 20% solids, for instance as described in U.S. Pat. Nos. 5,223,098, 6,024,790 and 6,045,657.

The bentonite may be applied to the cellulosic suspension as an aqueous bentonite slurry. Typically the bentonite slurry comprises up to 10% by weight bentonite. The bentonite slurry will normally comprise at least 3% bentonite clay, typically around 5% by weight bentonite. When supplied to the paper mill as a high solids flowable slurry usually the slurry is diluted to an appropriate concentration. In some instances the high solids flowable slurry of bentonite may be applied directly to the paper making stock.

The bentonite may be added to the cellulosic suspension either before or after addition of the amphoteric polymer of the invention. The bentonite may also be added simultaneously, (preferably separately), with the amphoteric polymer.

Desirably the siliceous material is applied in an amount of at least about 100 ppm by weight based on dry weight of suspension. Desirably the dose of siliceous material may be as much as about 10,000 ppm by weight or higher. In one preferred aspect of the invention doses of about 100 to about 500 ppm by weight have been found to be effective. Alternatively, higher doses of siliceous material may be preferred, for instance about 1000 to about 2000 ppm by weight.

Dosages in the paper industry are frequently expressed in the units kg/ton based on dry weight of the furnish. Expressed in these units the amount of siliceous material added to the furnish may range from about 0.2 to about 10 kg/ton; preferably about 1.0 to about 6 kg/ton; most preferably about 1.0 to about 4 kg/ton based on the dry weight of the furnish.

The weight to weight ratio of the amphoteric polymer to siliceous material may range from about 0.2:10; preferably 1:1 to 1:4; and most preferably 1:2. For example, the fixative or polymer may range from about 0.5 to about 2 kg/ton with the siliceous dosage ranging from about 1 to about 2 kg/ton.

For deposit control the siliceous material and the polymeric fixative are preferably added to the thick stock (about 2-4% cellulose concentration) during the papermaking process.

The amount of the free radical initiator used in the polymerization process depends on the total monomer concentration and the type of monomers used and may range from about 0.2 to about 5.0 wt % of the total monomer charge to achieve conversion of more than 99% of the total monomer.

The specific embodiments of this invention are illustrated by the following examples. These examples are illustrative of this invention and not intended to be limiting.

EXAMPLES

Synthesis of Polymers

Example 1 Synthesis of Amphoteric DADMAC Polymers 1-10 and DADMAC homopolymer Control

The procedure for making Polymer 1 is described in this example. Other polymers are made following the same procedure, but using different monomer ratios, initiator feeds and temperature to obtain polymers with different compositions and molecular weights. Molecular weights of the polymers are measured using the bulk viscosity or Brookfield viscosity (BV) at 20% polymer solids. A high 20% BV value indicates a high MW. Properties of the polymers synthesized are shown in Table 1.

A 1-liter reactor equipped with a condenser, a thermometer, a nitrogen inlet, and an overhead agitator is charged with 453.86 g of 66% monomer DADMAC, 15.8 g of acrylic acid, 59 g of deionized water and 0.15 g of Versene (Na₄EDTA). 35 g of a 25% NaOH solution is added slowly to the reactor at room temperature to neutralize the acrylic acid. The polymerization mixture is purged with nitrogen and heated with agitation to a temperature of 90° C. 36 g of a 14.5% ammonium persulfate (APS) aqueous solution was slowly fed to the reactor over 165 minutes. The reaction temperature is allowed to increase to above 100° C. and then maintained at 100 to 110° C. during the APS feed period. After the APS feed, the reaction mixture is diluted with deionized water to about 40% solids and held at 90° C. for about 30 minutes. Then an aqueous solution containing 5.6 g of sodium metabisufite is added over 40 minutes. The reactor is held at 90° C. for another 30 minutes to complete the polymerization (above 99% conversion). The polymer solution is diluted with sufficient water to about 35% solids. This product has a solids content of 35.3 wt. % with a 25° C. Brookfield viscosity of 8,800 cps and a 25° C. Brookfield viscosity at 20% solids (20% BV) of about 400 cps. The 20% BV is proportional to molecular weight of the polymer and therefore the data are used to compare the molecular weights of different solution polymers. TABLE 1 Copolymers of DADMAC, acrylic acid and acrylamide ²Viscosity, 20% BV at Sample M1/M2/M3* Solids cps 25° C., cps ¹Control  100/0/0 34.6% 7,850 410 Polymer 1   95/5/0 35.3% 8,800 400 Polymer 2   90/10/0 35.3% 8,850 400 Polymer 3   95/5/0 35.4% 15,700 630 Polymer 4   90/10/0 35.4% 15,560 625 Polymer 5   80/20/0 34.6% 39,800 1500 Polymer 6   60/40/0 34.6% 31,000 1300 Polymer 7   95/5/0 21.1% 2760 2180 Polymer 8   92/80 21.5% 2730 1960 Polymer 9 92.5/2.5/5 21.6% 2860 1990 Polymer 10   91/8/1 20.3% 2400 2240 ¹Homopolymer of DADMAC ²Viscosities of 1000 to 3000 cps, use spindle LV3 at 30 rpm; 3000 to 8000 cps use spindle LV3 at 12 rpm and 8,000 to 16,000 cp, use spindle LV3 at 6 rpm. *M1 = DADMAC; M2 = acrylic acid (AA); M3 = acrylamide Performance Evaluation

Commercial products listed in Table 2 are also used in the evaluation for comparison. TABLE 2A Existing commercial fixatives (EFC) products tested Product ID Polymer Chemistry Alcofix 269 Low MW DADMAC homopolymer Alcofix 110 High MW DADMAC homopolymer Alcofix 111 High MW DADMAC homopolymer Alcofix 159 Medium MW polyamine Alcofix 160 High MW polyamine Alcofix 158 Low MW polyamine ¹Alcofix 161 DADMAC copolymer ²Alcofix 505 DADMAC copolymer Raifix 120 Cationic starch ¹Copolymer of 95% DADMAC and 5% acrylamide. ²Copolymer of 50% DADMAC and 50% acrylamide.

A vacuum drainage filtrate turbidity test is used to demonstrate the performance of the amphoteric polymers of the present invention and commercial fixatives products and their ability to fix pitch, stickies and other contaminants onto fibre and therefore control and prevent these contaminants from deposition during paper making. The detailed test procedure is shown below.

-   1. About 250 mL of a 3-5% consistency furnish is measured into a     baffled Britt jar. Adequate mixing is provided with a IKA mixer set     to agitate at 1000 rpm. -   2a. The required amount of polymer is added to the agitated thick     stock and allowed to mix for 2 minutes. -   2b. Optionally, the required amount of siliceous material is added     to the agitated thick stock and allowed to mix for 2 minutes. -   3. The treated thick stock is then filtered through a Whatman 541     filter paper (11 cm diameter, coarse—retention for particles>20-25     microns) under vacuum. -   4. Vacuum filtration continues until the “wet line” just disappears     or approximately 200 mLs of filtrate is collected. -   5. Turbidity of the filtrate is measured with a suitable     turbidimeter. -   6. Cationic charge demand (CCD) of the filtrate is determined by     colloidal titration.

Dosage used is in weight of active polymer per ton of pulp solids (dry weight).

The lower the filtrate turbidity, the greater is the pitch and stickies control of the treatment employed and therefore the better performance of the polymer used.

Example 2

The samples tested in this example all have a relatively low molecular weight expressed by the 20% BV of about 400 cps. Testing is performed on 100% recycled old corrugated container (OCC) furnish from a linerboard mill experiencing serious stickies deposit problem. This example shows that with similar MW, the amphoteric DADMAC copolymer Polymer 1 performs better in the turbidity reduction than the DADMAC homopolymer control. Results in Table 2B for the Control, Polymer 1 and Polymer 2, demonstrate that the performance improvement with incorporation of the AA anionic component is diminished when the M content is above 10%. TABLE 2B 100% recycled Old Corrugated Container (OCC) furnish blank Turbidity, 379 NTU Dosage, kg/ton 1.0 2.0 5.0 Turbidity, NTU Control 1 (homopolymer 0% AA) 57 49 43 Polymer 1 (5% AA) 57 46 39 Polymer 2 (10% AA) 60 54 42

Example 3

The samples tested in this example all have a higher molecular weight expressed by the 20% BV of above 600 cps. Testing is performed on 100% recycle deinked pulp furnish from a paper mill. This example further demonstrates that the performance improvement with incorporation of AA anionic component is diminished when the AA content is above 10%. See Table 3A. A commercial fixative (Alcofix 159, a medium MW polyamine) commonly used for deposit control in paper mills is also included in the testing. Polymer 3 of the present invention gives significantly better performance in turbidity reduction than the commercial fixatives. TABLE 3A 100% recycled furnish deinked pulp (DIP) furnish blank turbidity, 578 NTU Dosage, kg/ton 0.2 0.4 0.8 Turbidity, NTU Commercial fixative (Alcofix 159) 126 73 50 Polymer 3 (5% AA) 99 63 41 Polymer 4 (10% AA) 176 104 49 Polymer 5 (20% AA) 149 105 51 Polymer 6 (40% AA) 159 101 50

Example 4

Performance on Coated Broke

Performance of the DADMAC copolymers of the present invention for white pitch control is evaluated on different types of coated broke. The samples are tested on the following three types of broke.

-   -   45# Pub Matte, a light-weight free sheet     -   38# DPO, heavy weight groundwood containing     -   70# DPO, heavy weight groundwood containing

For each dosage of polymer treatment, the turbidity and cationic demand of the filtrate is measured. The results of the study are shown in the Tables 4A, 4B and 4C. TABLE 4A 45# Pub Matte: Turbidity of treated furnish at different dosage (lb/ton on dry solids basis) Dosage (lb/ton) 0.4 0.8 1.2 1.6 2.4 Polymer 7 2635 511 176 110 Polymer 8 2792 396 194 120 Polymer 9 2558 414 166 68 Alcofix 110 2995 825 246 200 Alcofix 269 2011 322 248 Alcofix 159 1258 447 316

TABLE 4B 70# DPO: Turbidity of treated furnish at different dosage (lb/ton on dry solids basis) Dosage (lb/ton) 0.4 0.8 1.2 1.6 2.4 Polymer 7 110 57 44 31 Polymer 8 141 49 29 35 Polymer 9 88 56 31 31 Alcofix 110 170 87 58 46 Alcofix 269 157 130 97 Alcofix 159 110 87 72

TABLE 4C 38# DPO: Turbidity of treated furnish at different dosage (lb/ton on dry solids basis) Dosage(lb/ton) 0.4 0.8 1.2 1.6 2.4 Polymer 7 10372 4090 2246 302 Polymer 8 4894 605 131 56 Polymer 9 7556 2596 329 122 Alcofix 110 11368 5192 2172 184 Alcofix 269 2512 247 127 Alcofix 159 6856 2286 319

The test data on existing commercial fixative products (Alcofix 269, Alcofix 110, and Alcofix 159) are also obtained for comparison and show the benefit of using the copolymers of the present invention. The copolymers of the present invention give performance significantly better than all the commercial products tested.

Example 5

Performance on Deinked Pulp (DIP) Recycled Furnish.

The test data on recycled deinked pulp (DIP) are obtained to show performance of the amphoteric DADMAC copolymers over existing commercial fixatives products Alcofix 161, a coplymer of DADMAC and acrylamide. The new DADMAC-based amphoteric polymer samples give performance significantly better than the commercial products. Improvements of up to about 50% over a commercial DADMAC copolymer (Alcofix 161) in average turbidity reduction are obtained.

Filtrate turbidity (FT) results in Table 5 show DIP furnish treatment with amphoteric DADMAC copolymers and compare with furnish treated with a commercial DADMAC copolymer (Alcofix 161).

Lower FT indicates better performance for stickies deposit control. TABLE 5 % FT reduction Dosage(lb/ton) Average FT, over 1.0 2.0 3.0 4.0 NTU Alcofix 161 Alcofix 161 131 87 65 49 83 0 Polymer 1 111 64 52 45 68 18.1 Polymer 3 100 55 45 41 60 27.4 Polymer 7 98 48 48 34 57 31.3 Polymer 8 71 41 29 23 41 50.6

Example 6

Performance on TMP, DIP and TMP/DIP Mix Furnish.

Amphoteric DADMAC copolymers of the present invention are evaluated on three types of furnish (TMP, DIP and mix of DIP&TMP) from a paper mill together with nine commercial products. Various commercial fixative products included in the testing are 3 DADMAC homopolymers with different molecular weights, 2 copolymers of DADMAC and acrylamide with different monomer ratios and molecular weights, 3 polyepiamines with different molecular weights and structures, and 1 cationic starch. Of the 9 commercial fixatives tested, Alcofix 161, a DADMAC copolymer, performed consistently the best among the commercial products. Therefore, results of the amphoteric DADMAC copolymers of the present invention are compared only to those of Alcofix 161 to show their performance over existing commercial fixative products. As can be seen from Table 6A, B and C, the amphoteric DADMAC copolymers of the present invention perform significantly better than the best commercial fixative for all three types of furnishes. An improvement of greater than about 20 to about 74% turbidity removal over Alcofix 161 is observed using the amphoteric DADMAC copolymers of the present invention. TABLE 6A Filtrate turbidity (FT) of treated furnish with 100% TMP at different dosages (kg/ton on dry solids base). Turbidity of untreated furnish is 213 NTU. Dosage (kg/ton) Average % FT reduction 0.25 0.5 1.0 2.0 FT, NTU over Alcofix 161 Alcofix 161 154 120 80 43 99 0 Polymer 7 126 96 63 27 78 20 Polymer 8 116 95 57 23 73 24 Polymer 9 131 91 71 23 58 19

TABLE 6B Filtrate turbidity (FT) of treated furnish with 100% DIP at different dosage (kg/ton on dry solids base). Turbidity of untreated furnish is 218 NTU. Average % FT reduction Dosage (kg/ton) 0.10 0.2 FT, NTU over Alcofix161 Alcofix 161 100 41 71 0 Polymer 7 78 28 53 25 Polymer 8 62 25 44 38 Polymer 9 79 32 56 21

TABLE 6C Filtrate turbidity (FT) of treated furnish with 60% TMP and 40% DIP at different dosages (kg/ton on dry solids base). Turbidity of untreated furnish is 164 NTU. Average % FT reduction Dosage (kg/ton) 0.10 0.2 FT, NTU over Alcofix 161 Alcofix 161 125 103 114 0 Polymer 7 106 77 92 45 Polymer 8 90 64 77 74 Polymer 9 115 85 100 28

Example 7

Filtrate turbidity (FT) of treated furnish of 100% TMP at different dosages (kg/ton on dry solids basis) of fixative and bentonite.

The turbidity and total ester concentrations (a measure of pitch) are determined in the filtrate and compared in Table 7. The testing procedure is essentially the same as that preformed for the commercial fixatives shown in Table 2 except a 2% consistency furnish is tested and the residual ester, triglyceride esters and total ester pitch concentrations are determined using gas chromatography (GC).

The GC analysis was run on a DB-5HT 5m×0.25 mm×0.10 micron column, an Inlet temperature of 300° C. and an FID Detector temperature of 350° C. The heating program: Initial temp of 100° C. hold for 1 minute then increase 15° C./min up to 350° C. and hold for 15 minutes. TABLE 7 Filtrate turbidity (FT) of treated furnish of mechanical pulp at different dosages (kg/ton on dry solids basis). Polymer dosage Residual (solids Bentonite Centrifuged Ester Triglyceride Ester Pitch basis) dosage Turbidity Conc. esters Total Treatment Kg/ton kg/ton NTU (ppm) (ppm) (ppm) Blank 0 0 564 2.4 1.5 3.9 Alcofix 269 1 0 362 0.6 0.6 1.2 ¹Polymer 10 1.0 0 455 0.6 0.6 1.2 ²bentonite 0 2.0 398 1.3 1.2 2.5 bentonite 1.0 2.0 337 0.2 0.2 0.4 followed by Polymer 10 ¹Terpolymer of DADMAC, acrylic acid and acrylamide. ²Bentonite is supplied under the tradename HYDROCOL 2D1 from Ciba Specialty Chemical Corp. The HYDROCOL 2D1 was supplied as a 5% aqueous slurry based on the total weight of the aqueous slurry.

Example 8

Treatment of Coated Broke with Polymer and Bentonite

The furnish is primarily bleached TMP. The furnish is combined with about 12 to 20% coated broke and diluted to approximately 3% consistency using white water from the mill process. Bentonite was added first as a 5% aqueous slurry at a dosage of 1.5 kg/t then followed by polymer 10. Table 8 shows the improvement in turbidity when the amphoteric polymer is combined with bentonite. TABLE 8 Tubidity knockdown for coated broke Treatment Turbidity in NTU Blank 925 Alcofix 269 (0.4 kg/ton) 287 Polymer 10 (0.2 kg/ton) 240 Polymer 10 (0.8 kg/ton) + ¹bentonite (1.5 kg/ton) 130 ¹Bentonite is supplied under the tradename HYDROCOL 2D1 from Ciba Specialty Chemical Corp.

It should be understood that the above description and examples are illustrative of the invention, and are not intended to be limiting. Many variations and modifications are possible without departing from the scope of this invention. 

1. A method of controlling pitch and stickies deposition in papermaking which method comprises the step of adding to paper furnish prior to sheet formation a composition comprising an amphoteric polymer represented by the following structure (I)

wherein X⁻ is an anion; M⁺ is hydrogen, ammonium, sodium, or potassium; R is hydrogen or methyl; R₁ is methyl or ethyl; n is from about 70 to about 99.8 wt. %, m is from about 0.2 to about 30% and p is from 0 to about 30%, with n+m+p=100% based on the total weight of the amphoteric polymer.
 2. A method according to claim 1, wherein X⁻ is Cl⁻, M⁺ is Na⁺, n is from about 85 to about 98%, m is from about 1 to about 15%, and p is from 0 to about 10% by weight.
 3. A method according to claim 1 further comprising the step of adding a siliceous material.
 4. A method according to claim 3 wherein the amphoteric polymer is added to the paper furnish followed by addition of the siliceous material.
 5. A method according to claim 3 wherein the siliceous material is added to the paper furnish followed by addition of the amphoteric polymer.
 6. A method according to claim 3, wherein the siliceous material is an anionic microparticulate material.
 7. A method according to claim 3, wherein the siliceous material comprises material selected from the group consisting of silica based particles, silica microgel, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates and zeolites.
 8. A process according to claim 3 wherein the siliceous material is a swellable clay.
 9. A process according to claim 8 wherein the swellable clay is selected from the group consisting of hectorite, smectitites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites, and sepiolites.
 10. A method according to claim 2, wherein m is from about 1 to about 8%.
 11. A method according to claim 1, wherein p is from about 1 to about 8%.
 12. A method according to claim 1, wherein the amphoteric polymer has a molar ratio of n/m of about 1.2 or greater.
 13. A method according to claim 12, wherein the molar ratio of n/m is about 4 or greater.
 14. A method according to claim 1, wherein n represents a unit derived from a cationic monomer selected from the group consisting of diallyldialkylammonium compounds; m represents a unit derived from an anionic monomer or potentially anionic monomer selected from the group consisting of hydrolysed acrylamide, hydrolysed methacrylamide, acrylic acid, methacrylic acid and/or salts of acrylic acid or methacrylic acid.
 15. A method according to claim 14, wherein the anionic monomer is hydrolysed acrylamide.
 16. A method according to claim 14, wherein the anionic monomer is acrylic acid, methacrylic acid and/or salts thereof.
 17. A method according to claim 14, wherein the cationic monomer is diallyldiethylammonium halide or diallydimethylammonomium halide.
 18. A method according to claim 1, wherein the amphoteric polymer of formula (I) has a weight average molecular weight ranging from about 10,000 to about 20,000,000.
 19. A method according to claim 1, wherein the paper furnish contains thermal mechanical pulp, recycled pulp, coated broke, deinked pulp or mixtures thereof.
 20. A composition for pitch and stickies control in papermaking comprising a structure (I) according to claim 1 and optionally, a siliceous material. 